Get out your wallet
Once you've exhausted the no-cost option of just moving things around, the next steps involve spending additional money. The trick here is to spend wisely and get the maximum bang for your buck. This section will help you define the problem you're trying to solve, which should help guide your hard-earned money in the right direction.
AP or Client?
The first thing to consider is whether you should improve the access point or client end of the connection. The natural inclination is to focus on the AP, especially when your WLAN includes more than one client. But if you have only one, or maybe two wireless clients to deal with, don't rule out the client-based solutions in the next section . You may be surprised how much higher-gain antennas can cost for your AP, vs. how little new wireless client cards are going for!
And even in the cases where the cost of changing your wireless card or improving your access point are about equal, an upgrade of your client card to a current-generation model, may have other benefits such as multi-band access, or improved WEP-enabled speed.
The Centralized Approach
Most people, however,like to focus on beefing up their AP via either a different antenna or signal booster. Some gear-heads also play with boosting the transmit power on Atmel-based APs like the pre-v2.2 Linksys WAP11, SMC2655W, or Netgear ME102. Boosting the transmit power only is the least preferable way to go, because the "hacks" are generally not for beginners, but more importantly are only a one-way solution. Since wireless LANs require two-way communication between AP and client, you may not see the performance improvement you expect by making the signal stronger at only one end of the connection.
The advantage of the centralized approach is that - done correctly - it can benefit most, if not all of your WLAN's clients. This is a definite plus if you have a lot of clients to feed. The disadvantage is that it may improve your WLAN's range enough to make it more widely visible to clients that you don't want on your network.
If you're going to try an AP-boosting approach, your main choice is to use a higher-gain antenna, if your AP's antennas are attached via connectors. Not all 802.11b AP's have upgradeable antennas and if yours doesn't, you'll either need to choose another method or buy a new AP. If you decide to go this way, see the Upgrading your Antenna section.
NOTE: In general, you won't find single or dual-band 802.11a APs or wireless routers with removable antennas. This is due to tighter FCC rules for some of 11a's operating frequencies.
Another alternative for beefing up your AP that might take a little extra work is to use a signal booster. Although commonly used by Wireless ISPs for outdoor "backhaul" type links, Linksys recently brought signal boosting into the consumer market with its WSB24. Although FCC certified (and Linksys-supported) for use only with Linksys' popular WAP11 AP and BEFW11S4 wireless router, it can be used with any 2.4GHz AP if you're willing to provide your own cables. See the review for more info if you want to go this way.
There are two other approaches - wireless repeating and adding Access Points - but I'll save them for last. Instead, let's move on and take a closer look at how to improve the client side of things...